clags.h

A simple declarative command line argument parser, written in C.

Features

• Required, optional and flag arguments
• Typed arguments: bool, int8, uint8, int32, uint32, int64, uint64, double, path, size, time_s, time_ns
• Choice arguments: restrict values to a fixed set (like an enum)
• Custom parsing functions for user-defined types
• Native recursive subcommands

How to use

clags.h is an stb-style library, which means a single header file and headers and implementations separated by the CLAGS_IMPLEMENTATION header guard.
You can compile the library with any C99+ compiler. No further dependencies are required.

Example

#include <stdio.h>
#include <stdbool.h>

// This includes the function implementations and only has to be done once per translation unit
#define CLAGS_IMPLEMENTATION
#include "clags.h"

// Declare argument variables with optional default values
const char *input_file = NULL;
const char *output_file = "a.out";
bool warnings = false;
bool help = false;

// Declare all expected arguments
clags_arg_t args[] = {
    // Required (positional) arguments are parsed in the order they are defined here
    clags_required(&input_file, "input_file", "the input file"),
    
    // Optional arguments support both short and long flags
    // For long flags, both the `--output <file>` and `--output=<file>` syntaxes are supported
    clags_optional('o', "output", &output_file, "FILE", "the output file"),

    // Use flags to set boolean values on occurrence
    // Short flags can be standalone, or combined into multi-flags, e.g.: -abc
    clags_flag('w', "warnings", &warnings, "print warnings"),
    // This is a neat short-hand since the `--help` flags are so common
    clags_flag_help(&help),
};

clags_config_t config = clags_config(args);

int main(int argc, char **argv)
{
    // Parse the arguments using the previously defined rules, returns the config on error
    if (clags_parse(argc, argv, &config) != NULL){
        // Print an automatic usage, based on the defined config
        clags_usage(argv[0], &config);
        return 1;
    }
    // You can now use the set argument variables
    if (help){
        clags_usage(argv[0], &config);
        return 0;
    }
    printf("input: %s, output: %s, warnings:%s\n", input_file, output_file, warnings?"true":"false");
    return 0;
}

When run with this input:

./example --help

clags will print the following usage:

Usage: ./example [OPTIONS] [FLAGS] <input_file>
  Arguments:
    input_file               : the input file
  Options:
    -o, --output(=)FILE      : the output file
  Flags:
    -w, --warnings           : print warnings
    -h, --help               : print this help dialog and exit

For more advanced examples see the examples directory.